I remember reading here a while back where someone sonic checked a bunch of blocks and the later model blocks were no different than the earlier ones. Any of them can be thin, best bet is to have it checked. The myth that the later model blocks are too thin is just that...a myth.

CHIP
'70 hemicuda, 575" Hemi, 727, Dana 60
'69 road runner, 440-6, 18 spline 4 speed, Dana 60
'71 Demon, 340, low gear 904, 8.75
'73 Chrysler New Yorker, 440, 727, 8.75
'90 Chevy 454SS Silverado, 476" BBC, TH400, 14 bolt
'06 GMC 2500HD LBZ Duramax